This invention relates to dynamoelectric machines such as electric motors and generators.
In dynamoelectric machines having a commutating armature there is always present the problem of a cross-magnetizing field in the armature created by the load current therein. This problem is of little consequence in smaller machines, but when the machine size becomes greater than a few horsepower, and when maximum overload and broadest speed range are desired, it is advantageous to provide the machine with compensating windings coupled in series ith the armature. This tends to neutralize the cross-magnetization to the extent possible.
Problems occur in attempting to adapt a dynamoelectric machine to receive the compensating coils. While it is desirable to provide an effective orientation of the compensating coils, it is also important not to impair overall machine performance or unduly complicate the assemblage and disassemblage of the machine components.
It has been previously proposed to provide dynamoelectric machines with detachable pole shoes which contain slots for receiving the compensating coils. Exemplary of such a proposal are U.S. Rimkus Pat. No. 2,745,031, issued May 8, 1956 and U.S. Potter Pat. No. 2,679,607 issued May 25, 1954.
In Rimkus, the coil-receiving slots are intended to be open-ended and closed-sided. One assemblage problem posed by closed-sided slots is the difficulty involved in threading small-stranded conductors axially therethrough, an operation akin to attempting to push a rope from the end. In addition, Rimkus proposes that a groove be formed in the pole face for the reception of a cross-bar intended to serve in mounting the pole shoe to the yoke. Such a groove constitutes an interruption in the pole face and might tend to reduce the flux-conducting efficiency of the pole shoe.
The Potter patent proposes the use of a pole shoe having a main pole section and removable teeth which cooperate with the main pole section to define coil-receiving slots. The teeth are arranged to abut and support the coils. Inconveniences may arise in that removal of the excitation windings would require removal of the compensating windings, and vice-versa, in an arrangement where one set of mounting bolts functions to both secure the shoe sections together and attach the shoe to the yoke.
One serious problem associated with the presence of coils within pole slots concerns a tendency of the coils to oscillate, or vibrate, relative to the slot walls during machine operation. This behavior, besides being noisy, produces considerable wear on the coils and necessitates the use of relative thick insulation around the coils. Use of such insulation reduces the number of wires which can be placed in each slot and thereby places an unreasonable limitation on the compensating effect of the coil by limiting the number of ampereturns. Attempts have been made to eliminate this oscillation, as by inserting a non-magnetic, non-rigid compound between the slot walls and the coil. The effectiveness of this approach has been found to be of only temporary duration, however. Moreover, if a compound is used in slots which are slightly open at the pole face, parts of the compound could become detached, leaving depressions in the pole face and resulting in the introduction of loose debris within the machine.
Construction of the yoke portion of a dynamoelectric machine yoke may be conventionally accomplished by brazing together a series of laminated plates. This arrangement can be disadvantageous in that the brazing alloy typically occupies space which could otherwise be occupied by yet more plates, the addition of which would cut hysterisis losses and increase machine efficiency.
It is, therefore, a general object of the invention to provide novel methods and apparatus for minimizing or obviating problems of the sort previously discussed.
It is another general object of the invention to provide novel methods and apparatus for optimizing the performance of dynamoelectric machines.
It is a particular object of the invention to provide novel methods and apparatus for effectively resisting oscillation of compensating coils within dynamoelectric machine slots.
It is another object of the invention to provide a novel dynamoelectric machine characterized by simplified assemblage and disassemblage.
It is yet another object of the invention to provide a novel dynamoelectric machine which exhibits minimal hysterisis losses and maximum efficiency.